Ink applicator for screen printer

ABSTRACT

A downwardly open ink receptacle, surrounded by a cylindrical masking screen, has a downwardly convex bottom member of elastic material forming a discharge slot for the ink, this slot being spanned by one or more substantially inextensible reinforcing elements leaving clearances in line with the slot in order to give passage to the ink. The slot may be bounded by a pair of low-friction strips bearing directly upon the inner screen surface under pressure of a pair of weighting bars flanking the slot. The reinforcement can be a perforated foil, an insert with an undulating wire, or a series of axially spaced bolts.

United States Patent Zimmer Nov. 25, 1975 INK APPLICATOR FOR SCREEN PRINTER [76] Inventor: Peter Zimmer, Untere Sparchen 54,

[30] Foreign Application Priority Data May 30, 1972 Austria 4676/72 Feb. 21, 1973 Austria 1509/73 [52] U.S. Cl. 101/120; 101/123; 101/124; 118/406 [51] Int. Cl. B41F 15/44; 1305C 1/04 [58] Field of Search ..101/114,115,116, 119, 101/120, 121, 122, 123, 124,129; 118/406 [56] I References Cited UNITED STATES PATENTS 846,645 3/1907 Brooks 101/119 X 1,541,787 6/1925 Cadgene et a1... 101/116 K 2,445,666 7/1948 Ellam 101/119 2,697,397 12/1954 Bailey l0l/l19 3,752,071 8/1973 McKay 3,799,053 3/1974 Rabelow l0l/l25 Primary ExaminerClifford D. Crowder Assistant Examiner-R. E. Suter Attorney, Agent, or Firm-Ernest G. Montague; Karl F. Ross; Herbert Dubno [57] ABSTRACT A downwardly open ink receptacle, surrounded by a cylindrical masking screen, has a downwardly convex bottom member of elastic material forming a discharge slot for the ink, this slot being spanned by one or more substantially inextensible reinforcing elements leaving clearances in line with the slot in order to give passage to the ink, The slot may be bounded by a pair of low-friction strips bearing directly upon the inner screen surface under pressure of a pair of weighting bars flanking the slot. The reinforcement can be a perforated foil, an insert with an undulating wire, or a series of axially spaced bolts.

9 Claims, 15 Drawing Figures l I //l U.S. Patent Nov.25, 1975 Sheet1of9 3,921,520

US. Patent Nov. 25, 1975 Sheet20f9 3,921,520

FIG.2

U.S. Patent Nov.25, 1975 Sheet3of9 3,921,520

Sheet 5 of 9 US. Patent NOvQ25, 1975 US. Patent Nov. 25, 1975 Sheet6of9 3,921,520

U. S.. Patent Nov. 25, 1975 Sheet8of9 3,921,520

FIG.

FIGJO US. Patent Nov. 25, 1975 Sheet9of9 3,921,520

INK APPLICATOR FOR SCREEN PRINTER CROSS-REFERENCE TO RELATED APPLICATION This application relates to subject matter disclosed in my copending application Ser. No. 320,739 filed 3 Jan. 1973.

FIELD OF THE INVENTION My present invention relates to a dyestuff applicator for a printing machine of the type wherein a perforated cylindrical screen is rotatable about a horizontal axis and surrounds a housing forming an axially extending gap just above the nadir of the screen for the controlled discharge of printing liquid (referred to hereinafter as ink) through the perforations of the screen onto a substrate for imprinting the latter in accordance with a predetermined pattern.

BACKGROUND OF THE INVENTION In may above-identified copending application I have disclosed an applicator of this type wherein two sealing strips are weighted down by two parallel rods which flank the discharge gap and are attracted downwardly by a magnetic force.

In this type of applicator, in which no positive connection exists between the two strips forming the discharge gap, there arises the problem of maintaining the width of that gap essentially constant against the stresses which tend to vary that width during operation.

OBJECT OF THE INVENTION The object of my present invention, therefore, is to provide means for stabilizing the gap width while effectively preventing outward leakage of the printing liquid from the region of the gap onto adjoining portions of the inner screen surface.

SUMMARY OF THE INVENTION I realize this object, in accordance with my present invention, by providing a receptacle for the printing liquid with a cylindrically curved downwardly convey bottom member of elastic material forming a discharge slot or gap parallel to the cylinder axis, the underside of this bottom member being closely spaced from the surrounding apertured masking screen, and securing substantially inextensible reinforcing means to that bottom member, the reinforcing means spanning the discharge slot for preventing its enlargement while leaving clearances for the passage of printing liquid from the receptacle through that slot.

BRIEF DESCRIPTION OF THE DRAWING The above and other features of my invention will now be described in detail with reference. to the accompanying drawing in which:

FIGS. 1 and 2 are cross-sectional views, taken respectively on the lines I I and II II of FIG. 5, of an ink applicator embodying my present invention;

FIG. 3 is a plan view of a perforated reinforcing foil partially closing a discharge slot at the bottom of the applicator housing of FIGS. 1 and 2;

FIG. 3a is a'fragmentary cross-sectional view drawn to a-large scale and showing details of the foil of FIG.

FIG. 4 is a side-elevational view of the applicator of FIGS. 1 and 2; l

FIG. 5 is a view similar to FIG. 4, drawn to a larger scale and with parts broken away;

FIG. 6 is a top view of the right-hand end of the applicator, drawn to a still larger scale;

FIG. 7 is a cross-sectional view of another applicator according to my invention;

FIG. 8 is a view similar to FIG. 7, illustrating a modification;

FIG. 9 is a further cross-sectional view illustrating, somewhat schematically, an alternate embodiment;

FIGS. 10 and 11 are plan views similar to FIG. 3, showing modified reinforcements for the bottom of the applicator;

FIGS. 12 14 are fragmentary cross-sectional views of the applicator bottom, illustrating further modifications.

SPECIFIC DESCRIPTION In FIGS. 1 and 2 I have shown a printing-ink applicator according to my present invention whose housing 1 is reinforced by two profiled tubes 2 to minimize deformation of the lateral housing walls 3 as a result of the static pressure of the printing liquid or ink within the housing. The ink flows through a supply tube 5 and openings 6 into the applicator housing. In FIG. 1 the ink-supply openings 6 are shown overlain by ports 7 in the housing 1 which are covered by strips 8. If necessary, the clogged ink openings 6 can be cleaned through the ports 7. A screw 9 opens a throttled passage through a vent hole 10 during the entire operation of the applicator, the hole 10 having a diameter of about 4 mm. Normally a small quantity of ink flows out of the applicator through this vent hole. Since the printing ink may carry air bubbles along with it, it might happen after a sufficiently long period of operation that the applicator is filled to a large extent with air, which always accumulates in the upper part of the housing 1. This entrained air exits through the vent hole 10, so that the operation of the applicator will not be impeded by accumulating air. The applicator is surrounded by a cylindrical masking screen 11 which it closely approaches in the region of its nadir 12. The bottom of the applicator housing above the screen 11 comprises a plate 13 of para rubber bearing upon a nickel foil 14 which in turn rests on the screen 11 in the contact area 12. In order to intensify the contact pressure, round bars 15 of magnetizable material are disposed on the elastic plate 13 and are held in a predetermined relative position by straps 16 having recesses 17. The nickel foil 14 and the plate 13 are fastened by screws 19 to the bottom of housing 1. The housing 1 is furthermore so stiffened by the straps 16 and reinforcing segments 20 that it cannot be deformed. An intermediate region between straps 16 and segments 20 is unobstructed so that a free flow of the ink in the longitudinal direction of the applicator housing is facilitated. The illustrated mounting of plate 13 and foil 14 permits a tight, resilient application of the nickel foil 14 to the screen 11. Of course this foil 14 could also be made of some other material, as for instance a sheet of tombak, copperberyllium bronze, or the like. The round bars 15 are pressed against the stack formed by plate 13, foil 14 and screen 11 by an electromagnet 22 located below the screen 11. The contact pressure of the foil 14 against the screen 11 and thus the lateral sealing of a discharge gap 27, flanked by the bars 17, is thus jointly produced by the natural elasticity of the resilient metal foil 14 and the rubber plate 13, by the weight of the bars 17 supplemented by the magnetic force, and by the hydrostatic pressure of the ink within the housing. Gap 27 allows the ink to pass through pattern-forming apertures in masking screen 11 to an underlying substrate to be imprinted.

The ink-emitting holes 6 located near the ends of screen 11, one of which is visible in FIG. 2, are controlled by associated throttle screws 23. These holes 6 can be opened by a slight turning of the screws 23 which, as -will be explained later on in connection with FIG. 3, serve to regulate the outflow of the printing ink.

As shown in FIG. 3, the nickel foil 14 has coarse perforations 25 in the region of the discharge gap 27, which is narrower than the contact area 12. These perforations are preferably produced by punching, the nickel foil 14 being so mounted that the deformation or burr 24 due to the punching of the holes 25 faces upwardly, as shown in FIG. 3a. This prevents the clipping of small hairs of the substrate to be imprinted which extend through the perforations 25 into the rotating screen 11 and which, when cut, would dirty the inner wall surface of the screen. Foil 14, spanning the gap 27 defined by the downwardly convex bottom member 13 of the applicator housing 1, serves as a substantially inextensible reinforcing means which prevents the gap from spreading.

In FIGS. 4 and 5, where the same reference numbers are used as in the preceding Figures, the screen 11 is shown provided at opposite ends with heads 28 which are placed in rotation by means of gears 29 and 30. The driving torque comes from a power shaft (not shown) within gear boxes 31. The left end 32 of the ink tube 5, journaled in a bearing 33, is accessible for cleaning upon removal of a plug 34. The right end 35 has an elbow 36 with threads 37 for attachment to a feed line not shown.

The ink openings 6 are arranged in the center of the housing 7 within a narrow .region 39, so that identical flow paths are present for the ink at opposite ends 40 of the housing.

The rubber plate 13 is fastened to flanges 41 at the housing ends 40 by means of strips 42 and screws 43.

As can also be noted from FIG. 5, throttle screws 23 are disposed in the end regions of the applicator housing 1 so that any drop of pressure in either of these regions can be counteracted by slightly retracting these screws 23 to increase the controlled flow of the ink toward that end of tube 5.

FIG. 6 is a plan view of the right-hand end 40 of the housing, showing the vent hole formed in a nipple 44 which is screwed into that end of the housing 1. A tubular connection 45 links the nipple 44 with a thin guide hose 46 which returns the ink emerging from the throttled vent hole 10 together with any entrained air to the ink reservoir.

In the embodiment of FIG. 7, printing ink is supplied via the interior 102 of a tube 101 under a hydrostatic pressure which is produced by a pressure accumulator, an elevated ink container, a pump or the like, located outisde of a surrounding printing screen 103. The ink passes via apertures 104 of supply tube 101 into bores 105 of an elastic base 106 consisting, for instance, of rubber. This base 106, forming part of a downwardly convex bottom member, is held by guides 107 and 108 to the ink tube 101 serving as a liquid receptacle. The guide 108 is constructed as a lateral reinforcement preventing excessive bending of the base 106 in the direction of the arrow 109, i.e. the direction of the transport of a substrate 111 to be imprinted. The screen 103, during the printing operation, turns counterclockwise as indicated by an arrow and moves synchronously over the surface of the advancing substrate 111. Tangential bending forces exerted on the base 106 as a result of friction are resisted by an extension 112 of the guide 108. Stiffening plates 113 take up the not insignificant forces occurring there and transmit them via the ink tube 101 to the bearing structure lying outside the screen 103.

From the bores 105 the printing ink passes into a distributing channel 114 in which the equalization of liquid pressure takes place before the ink flows via a discharge gap 115 through the screen 103 into the underlying substrate 111. The gap 115 is a slot bounded by two edges 116 and 117 of a pair of low-friction strips 136, 137 (see also FIG. 8) which are held together by reinforcing bolts 118 disposed thereabove. These bolts are of relativelysmall diameter and have heads 119 which, through the intermediary of a washer 120, bears upon the right-hand side of the inverted-U-shaped lower part of base 106 while a nut 121, acting through another washer 122, engages the left-hand side of that part. Over the entire length of the applicator there are provided a series of such bolts, spaced along the screen axis, which together insure the maintenance of a practically constant width 123 of the slot 115. Within the inkdistributing channel 114 the bolts 118 are received in spacing sleeves 124 which keep the two walls of that channel a predetermined distance apart. The bolts 118 and their spacing sleeves 124 are advantageously made of an acid-resistant, stainless high-grade steel. However, they can also be made of a relatively nonextensible, thermoplastic or thermosetting resinj for example, polyamide or polyacetal is well suited for this purpose.

In FIG. 8 the same reference numbers are used as in FIG. 7. The flexible base 106 of this embodiment is limitedly movable in vertical direction with respect to the ink tube 101. The conduits 105 of FIG. 7 hav'ebeen replaced by aligned nipples 126 and interconnected by a length of corrugated and therefore flexible tube 127 which may consist of rubber, high-grade steel or plastic defining a fluidtight feed channel between the ink tube 101 and the base 106. Brackets 128 and 131, articulated to each other by a link 129 and pivot'pins 130, hold the base 106 in place upon rotation of the screen in the counterclockwise direction indicated by the arrow 110. The nipples 126 are fastened to the base 106 by means of a cover strip 132 which has flexural elasticity. The rubber body 133 of the base 106 can be bonded to the covering strip 132 by vulcanization or cementing. In its lower region the base 106 has a nonextensible reinforcing foil 134 provided with a perforated zone 135 at its center. This foil can be a'strip of, for instance, galvanized or noble sheet metal or of a substantially nonextensible plastic material in which the holes 135 are produced by punching. This foil 134 is fastened to the rubber body 133 by bonding or vulcanization. Bonded to the underside of sheet 134 are the two aforementioned low-friction strips 136 and 137 whose separation defines the width 123 of the slot 115, the foil 134 being sandwiched between thesestrips-and the arms of the inverted *U" formed by base 133. The two slot edges 116 and 117 are in this case held apart by the foil 134 at an invariable distanceso that the slot width 123 cannot be changed by the frictional forces occurring between the rotating screen 103 and the slide coverings 136 and 137. Pressure tests carried out with such devices have established a remarkable uniformity of the depth of color and penetration of the substrate printed in this manner. The perforations 135, if suitably distributed, do not impair that uniformity, particularly if the discharge gap 115 is disposed below them.

The applicator of FIG. 8, of course, also be modified as, for instance, by providing the ink tube 101 with a guide in which the base 106 is vertically displaceable.

FIG. 9 shows another embodiment in which a fluidtight container 138 is filled with printing liquid via inkinlet openings 139 provided at its ends. In its lower region the container 138 is closed by an elastically flexible sheet 140 preventing the outflow of liquid from this container downward through the screen 103 into a region other than that of the slot 1 15. The sheet 140 preferably consists of a synthetic rubber so as to be yieldable in vertical direction in case of unevenness of the substrate. This elastic sheet material, however, also causes a certain extensibility in tangential direction tending to change the width of the discharge slot 115 by reason of the unavoidable frictional forces between the screen 103 and the slide coverings 136 and 137, cemented onto the foil 140, the slot 115 registering with a continuous slit 141 formed in that foil. I therefore reinforce the bottom of receptacle 138 by inserting a sinusoidally bent steel or plastic wire 142 above the foil 140 in the region of the slot 115 and the slit 141, the wire being fastened to the foil 140 by means of an elastic polymer 143. The undulating wire insert 142 is so arranged, as best seen in FIG. 10, that its individual turns point in the direction of rotation of the screen. The frictional forces exerted in the same direction on the slide coverings 136 and 137, transmitted to the foil 140, can then no longer change the width 123 of the slot 115 since this width is maintained constant under all conditions by the substantially inextensible wire insert 142. That insert could also be replaced by a coarsemesh fabric.

FIG. 11 shows an alternate arrangement wherein the reinforcement 142 has been replaced by a perforated metal strip 144 fastened at the same place as the wire insert 142 to the foil 140, again with the aid of a polymer or vulcanizate 143. For better adherence of this polymer, which is applied in liquid condition to the metal strip and the foil 140 located below it, the metal strip 144 is provided in its lateral regions with oblong perforations 145. In order to assure a distribution of the ink which is as uniform as possible, the diameter 147 of each individual hole 146 of the perforated central strip zone bears a predetermined ratio to the center-tocenter distance 148 between these holes. That ratio advantageously has the approximate value of 1:2 cos 30 3 The center points of the holes then neatly fill a network of lines of a hexagonal raster. If the physical webs remaining between the holes are not larger than to percent of the hole diameter, very uniform ink-passage conditions result.

As shown in FIG. 9, the elastic foil 140 is fastened tightly to the container edges 149 between clamping strips 150 and flanges 151.

FIG. 12 shows another modification wherein the elastic foil 140 is urged by the ink pressure or other means against a thin metal diaphragm 152, located below it, which has a perforated zone 135 approximately conforming to the patternof holes 146 shown in FIG. 11. This metal diaphragm l 52.bears the two slide strips 136 and 137 which assure low-friction contact between the screen 103 and the, convex bottom of the applicator and which again form an ink-distribution channel here very narrow in the region of the slot 115. This ink-distribution channel is, however, entirely sufficient, with a very small mesh size of the perforations 135, to distribute the printing ink uniformly.

FIG. 13 shows that it is also possible to provide the perforated zone 135, located between the two slot edges 116 and 117, in the foil itself. With this arrangement, also, very good results can be obtained although the uniformity of color is not as high as in the case of a diaphragm of metal or thermosetting plastic bridging the two slot edges 116 and 117 as shown in FIG. 12.

FIG. 14, finally, shows an embodiment in which the elastic foil 140 is provided with a single low-friction strip 153 provided with the perforated zone 135. Since the strip 153 generally consists of a readily slidable but not very extensible material which has a certain flexibility only by virtue of its small thickness, a quite satisfactory connection of the two slot edges 116 and 117 is assured; upon prolonged operation, however, a certain impairment occurs since the slide covering 153, of course, wears so that the reinforcement spanning the two edges 116 and 117 becomes weaker while the effective stresses remain the same. Eventually, there is reached a condition of wear in which the remaining thickness 154 of the slide covering 153 is no longer sufficient to withstand the frictional forces.

The present invention is not limited to the embodiments described and illustrated. Thus, the variants shown in FIGS. 12 to 14 can be used also in connection with the types of applicator shown in FIGS. 7 and 8. The foil 140 is then replaced by the rubber body 133 of the base 106. It is also possible to cover the bottom of the applicator housing contacting the substrate, such as the arms of the bodies 106 and 133 in FIGS. 7 and 8, with a rigid sheath, e.g. steel plates interconnected via a tubular body which encloses the ink tube. In this way the slot width is also kept constant.

Another possibility of keeping the slot width constant consists in providing slits interrupted at intervals by webs either in a covering sheet or else in the bodies 106 and 133. The bottom member defining the discharge gap can be integral with the webs in that case. A grate could be disposed both inside and outside the outlet proper.

It is also advantageous if the entire applicator can be swung around the axis of the ink tube, preferably by when the machine is stopped so that the substrate is not dirtied and the ink can be practically completely drained from the applicator housing.

Another advantage of the applicator construction in accordance with my invention is that inks with readily volatile solvents can also be used without any danger of thickening since the liquid receptacle is closed on all sides.

I claim:

1. In a printing machine, in combination:

a receptacle for printing liquid provided with a cylindrically curved, downwardUy convex bottom member of elastic material forming a discharge slot for said liquid parallel to the cylinder axis;

an apertured masking screen underneath said receptacle substantially concentric with and closely spaced from the underside of said bottom member; and

substantially inextensible reinforcing means secured to said bottom member and spanning said slot for preventing its enlargment, said reinforcing means leaving clearances for the passage of said liquid from said receptacle through said slot.

2. The combination defined in claim 1 wherein said reinforcing means comprises a flexible perforated foil overlying said slot.

3. The combination defined in claim 1 wherein said members further comprises an insert of undulating wire extending predominantly in a direction perpendicular to said slot.

4. The combination defined in claim 1 wherein said reinforcing means comprises a series of axially spaced bolts.

5. The combination defined in claim 1 wherein said receptacle has a generally cylindrical body and said member forms a base underlying said body with freedom of limited relative motion,'said base being provided with conduit means for supplying said printing liquid, said conduit means extending from said slot to the interior of said body.

6. The combination defined in claim 5 wherein said conduit means comprises resilient tubing.

7. The combination defined in claim 5 wherein said base has a cross-section substantially of inverted-U shape transverse to said axis, said reinforcing means spanning the arms of the U.

8. The combination defined in claim 7 wherein said reinforcing means comprises a flexible perforated foil secured to said arms, said member further including a pair of low-friction strips underlying said arms with confronting edges bounding said slot.

9. The combination defined in claim 8 wherein said foil is sandwiched between said arms and said strips. 

1. In a printing machine, in combination: a receptacle for printing liquid provided with a cylindrically curved, downwardly convex bottom member of elastic material forming a discharge slot for said liquid parallel to the cylinder axis; an apertured masking screen underneath said receptacle substantially concentric with and closely spaced from the underside of said bottom member; and substantially inextensible reinforcing means secured to said bottom member and spanning said slot for preventing its enlargment, said reinforcing means leaving clearances for the passage of said liquid from said receptacle through said slot.
 2. The combination defined in claim 1 wherein said reinforcing means comprises a flexible perforated foil overlying said slot.
 3. The combination defined in claim 1 wherein said members further comprises an insert of undulating wire extending predominantly in a direction perpendicular to said slot.
 4. The combination defined in claim 1 wherein said reinforcing means comprises a series of axially spaced bolts.
 5. The combination defined in claim 1 wherein said receptacle has a generally cylindrical body and said member forms a base underlying said body with freedom of limited relative motion, said base being provided with conduit means for supplying said printing liquid, said conduit means extending from said slot to the interior of said body.
 6. The combination defined in claim 5 wherein said conduit means comprises resilient tubing.
 7. The combination defined in claim 5 wherein said base has a cross-section substantially of inverted-U shape transverse to said axis, said reinforcing means spanning the arms of the U.
 8. The combination defined in claim 7 wherein said reinforcing means comprises a flexible perforated foil secured to said arms, said member further including a pair of low-friction strips underlying said arms with confronting edges bounding said slot.
 9. The combination defined in claim 8 wherein said foil is sandwiched between said arms and said strips. 